The present invention relates to an integrated circuit package and, more particularly, to a ball grid array substrate package that is sequentially built and accommodates at least one integrated circuit.
There have been several generations of integrated circuit packages used to mount an integrated circuit. Recently, development of one such generation known as a ball grid array substrate package has exhibited several advantages over earlier generations of integrated circuit packages. Earlier generations of integrated circuit packages include ceramic and metal packaging, each of which are expensive and difficult to manufacture. The advantages associated with the ball grid array substrate package generally include: (1) eliminating the need to route package leads to the outer edges of the integrated circuit package; (2) permitting smaller packages and closer spacing of packages mounted to the same printed circuit board; and (3) shortening interconnect lengths to improve electrical performance.
Ball grid array substrate packages have been further classified into either enhanced ball grid arrays or micro ball grid arrays. The micro ball grid arrays are typically used with integrated circuits having a relatively low number of inputs and outputs. Such integrated chips include various memory chips. Typically the micro ball grid array is constructed as a single layer of tape having dimensions similar to that of the integrated chip.
The enhanced ball grid arrays are used with integrated circuits that generate more than 3 watts or have a relatively large number of inputs and outputs. A relatively large number of inputs and outputs is in the range 300 through 1000. The integrated circuits used in conjunction with enhanced ball grid arrays are generally application specific integrated circuits, digital signal processors or microprocessors.
An example of an enhanced ball grid array package is briefly discussed below and disclosed in U.S. Pat. No. 5,583,378. The ""378 patent issued to Marrs et al. on Dec. 10, 1996, and is assigned to Amkor Electronics, Inc.
Referring to FIG. 1, there is illustrated a cross-sectional view of an enhanced ball grid array package 100, an integrated circuit 102 and a thermal conductor 104 all of which are described in the ""378 patent. The thermal conductor 104 is typically a thin layer (i.e. 0.127 to 0.254 millimeters thick) of copper that covers the entire outer surface of the enhanced ball grid array package 100.
The thermal conductor 104 is attached to an interconnection substrate 106 by an adhesive layer 108. The interconnection substrate 106 is a multi-layered printed circuit board laminate having a well region 110 in which the integrated circuit 102 is positioned. The integrated circuit 102 may be directly attached to a surface of the thermal conductor 104 or have an optional adhesive layer 112 located therebetween.
The interconnection substrate 106 is alternately composed of at least one insulating layer 114 and at least one conductive trace layer 116 manufactured by well known methods. The number of insulating layers 114 and conductive trace layers 116 depends on the type of integrated circuit 102, the electrical design requirements, and the number of circuit interconnections required. Insulating layers 114 and conductive trace layers 116 are laminated together with epoxy resin. Conductive vias or plated through-holes 118 are then drilled or laser ablated, and plated to form conductors for electrical connections between multiple conductive trace layers 116.
A soldermask layer 120 is applied over the outermost conductive trace layer 116 and functions as an insulator. The soldermask layer 120 further includes a plurality of electrical contacts 122 that are formed by creating selective openings in the soldermask layer 120. The electrical contacts 122 are typically plated with nickel and gold and are electrically connected to the integrated circuit 102. The connections between the electrical contacts 122 and the integrated circuit 102 start with the electrical contacts that are connected by the conductive vias 118 to various conductive trace layers 116, thereafter, a plurality of bond wires 124 connect the conductive trace layers to the integrated circuit.
A plurality of solder balls 126 are attached to the electrical contacts 122 such that the enhanced ball grid array package 100 can electrically communicate with a larger electronic system such as a printed circuit mother board (not shown).
As described earlier, the integrated circuit 102 is positioned in the well region 110 which may be filled to a predetermined level with an insulating encapsulant material 128. The insulating encapsulant material 128 is typically an epoxy based plastic resin that functions to protect the integrated circuit 102 and the plurality of bond wires 124 from the outside environment.
Low yield and high manufacturing costs are disadvantages associated with the current enhanced ball grid array package 100, because glass reinforced epoxy laminate is used in the interconnection substrate 106. In addition, the current enhanced ball grid array package 100 is highly susceptible to problems during the manufacturing process such as warpage, cosmetic defects, and unreliable application of nickel and gold onto the electrical contacts 122.
Furthermore, the application of nickel and gold to the electrical contacts 122 requires a bussing network that utilizes valuable space located externally of the interconnection substrate 106. The bussing network also requires that the solder balls 126 be coated with gold, where a problem may occur when using dissimilar metals in connecting the enhanced ball grid array 100 to the printed circuit mother board that has connections typically manufactured from copper.
Accordingly there is a need for a new generation of ball grid array substrate packages that are constructed by a manufacturing process using sequential build technology. There is also a requirement to position at least one integrated circuit within a corresponding cavity formed within a metal core of the ball grid array substrate packages. These and other needs are satisfied by the ball grid array substrate package of the present invention.
The present invention is an enhanced substrate package suitable for use with a ball grid array and a method for manufacturing the same, wherein the substrate package includes a metal core having a first surface and a second surface opposite the first surface. The metal core further includes at least one cavity in which at least one integrated circuit is positioned. A dielectric layer is secured to the first surface of the metal core and includes a die cavity formed therein. Thereafter, a conductive seed layer is chemically deposited to exposed portions of the dielectric layer and the first surface of the metal core. Adjacent to the conductive seed layer, a circuit is electrolytically and selectively formed within a first circuit pattern. An electrically resistive soldermask layer may be disposed on the dielectric layer and the circuit.
According to one aspect of the invention, the first surface has an adhesion promoting electrically conductive surface layer which permits the dielectric layer to be directly attached to the core without the need for an adhesive.
According to another aspect of the invention, the dielectric layer has a outer recessed edge located along at least a portion of an outer perimeter of the metal core and/or an inner recessed edge located along at least a portion of an outer perimeter of said cavity. In each instance, the recessed edge can be covered by the soldermask layer and thereby protected from moisture ingress.
In addition, the substrate package of the invention may further include a via or through-hole extending through the thickness of the dielectric layer and the soldermask layer, and an electrical conductor extending through the via from an outer surface of the soldermask layer to an upper surface of the adhesion promoting layer, whereby the metal core can be grounded through the land.
According to the present invention there is provided a ball grid array substrate package manufactured using sequential build technology. Also in accordance with the present invention there is provided a ball grid array substrate package having a bonding area that is electrolytically and selectively formed over a portion of the circuit. In accordance with the present invention there is further provided a ball grid array substrate package the uses a differential etch process to remove a conductive seed layer. Further in accordance with the present invention there is provided a ball grid array substrate package having a bonding area selectively formed with an inner layer of nickel and an outer layer of gold in a predetermined location.
A process for manufacturing a ball grid array substrate according to the invention includes the steps of oxidizing a first surface of a metal core with an adhesion promoter, applying a dielectric to the first surface of the metal core, creating at least one die cavity within the dielectric to expose a portion of the first surface of the metal core, metallizing a conductive seed layer to an exposed portion of the dielectric layer and to at least an exposed portion of the first surface of the metal core, and electrolytically forming a circuit. Manufacturing improvements provided by the invention further include forming successive layers electrolytically without use of an adhesive, and a semi-additive metallization technique which applies a seed layer in a thickness sufficient to form a circuit thereon, then later removes the seed layer after the circuit has been formed. These and other aspects of the invention are discussed in the detailed description that follows.